In steam turbines, a nozzle box is used to change the direction of steam flowing into the turbine from a generally radial direction to an axial direction for flow through the various stages of the turbine. The nozzle box surrounds the turbine rotor and packing ring seals are typically used to seal between the nozzle box and the rotor. Because of reduced clearance with the rotor, certain nozzle boxes have required a split packing ring holder assembly to retain the shaft seal packings, i.e. the sealing segments about the rotor. These prior packing ring holder assemblies each included a relatively thin annular piece terminating at axially opposite ends in radially extending flanges. A second piece of the holder assembly bolted and clamped one of the flanges of the first piece between the second piece and the nozzle box. The first and second pieces had axially extending flanges which cooperated with a generally dovetail shaped sealing segment to secure the sealing segment in sealing relation to the rotor. Each sealing segment carried labyrinth seal teeth for sealing relative to the rotor.
Because of the limitations of space between the nozzle box and the rotor, the packing ring tended to become unstable. The packing ring segments were generally spring biased toward the rotor and the springs tended to be off center. The thin annular ring also had a tendency to bend. As a consequence, the seal packing was unstable, tended to vibrate, increased the difficulty of installation in the field and had longer outage times during repair and replacement. Consequently, there has developed a need for a packing ring sealing assembly for a steam turbine having, inter alia, increased sealing segment stability, easier installation and shortened outage time.